For bonding between terminal members of compact electric parts or between a terminal member and a conductive wire, TIG welding process using a nonconsumable torch electrode (tungsten electrode rod) has been used in many cases.
A technique of starting arc discharge in the TIG welding process using the nonconsumable torch electrode employs the following three types of systems: a high-frequency generation system of which insulation breakdown is caused by generating high-frequency discharge at the time of the start to make a transition to arc; a direct-current high voltage application system of which insulation breakdown is caused by applying a high voltage of generally 10 kV or more between a torch electrode and a base material, that is, a bonding workpiece, only at the time of start to make a transition to arc; and a touch start (or lift start) system of which a torch electrode contacts a bonding workpiece, current carrying is started without using a high frequency, and then the torch electrode and the bonding workpiece is separated, thereby generating arc discharge. With regards to the high-frequency generation system and the direct-current high voltage application system, it has been considered as undesirable in many welding sites that both systems require a high-voltage power supply for generating either a high frequency or a high voltage and thereby increase the cost of welders, and that the high-frequency or high-voltage noise cause adverse effects on the electric parts of the electric circuits and peripheral electronic equipment. In this regard, the touch start system which does not require a high-frequency power supply nor a high-voltage power supply allows for cost reduction of welders, and moreover, causes no problems relating to high-frequency noise (PTL 1).